4000 Quattro Question

["Guillermo S. Christensen" <gchriste@cap.gwu.edu>]

I have two questions that I am hoping other Quattro owners may be able to
address.  First, a few years back while I was in Germany a friend of mine
who owned a Quattro coupe, would routinely lock the center differential
when driving at moderately high speeds (approx. 120-140 km/h) on a WET
autobahn.  This, he claimed, settled the car down and improved braking at
higher speeds in the wet.  Is doing the same thing a good idea on an '84
4000 Quattro (I am a relatively new owner, still waiting for the first
snowfall to try out the 4wd advantage). 

Second question:  Today the odometer in my Audi stopped working (both odo
and trip meter are kaput, I assume they are connected).  The speedometer
works OK, although it has for some time "wavered" erratically at the low
speed (10-20mph) range, but is fine over 20 mph.  Any ideas as to what
could be wrong with the odometer?  thanks.